1. Technical Field of the Invention
The present invention relates generally to semiconductor devices and, more particularly, to a concentrated photovoltaic (CPV) receiver package or module wherein a conductive paste is used as an alternative to wire bonds or braided ribbon/mesh connectors to facilitate the electrical connectivity between the photovoltaic die of the module and the conductive pattern of the underlying substrate thereof.
2. Description of the Related Art
Photovoltaic cells or dies are a well known means for producing electrical current from electromagnetic radiation. Traditional photovoltaic cells comprise junction diodes fabricated from appropriately doped semiconductor materials. Such devices are typically fabricated as thin, flat wafers with the junction formed parallel to and near one of the flat surfaces. Photovoltaic cells are intended to be illuminated through their so-called “front” surface. Electromagnetic radiation absorbed by the semiconductor produces electron-hole pairs in the semiconductor. These electron-hole pairs may be separated by the electric field of the junction, thereby producing a photocurrent. Currently known photovoltaic cells typically have a generally quadrangular (e.g., square) configuration defining four peripheral side edges, and include a pair of bus bars which are disposed on the top or front surface and extend along respective ones of an opposed pair of the side edges. The bus bars are used to facilitate the electrical connection of the photovoltaic cell to another structure, as described in more detail below.
There is currently known in the electrical arts semiconductor devices known as CPV receiver die packages or modules. Currently known CPV modules typically comprise a ceramic substrate having a conductive pattern disposed on one side or face thereof. Attached to the substrate and electrically connected to the conductive pattern are electrical components, including a pair of preformed wire connectors and a packaged diode. Also attached to the substrate and electrically connected to the conductive pattern thereof is a CPV receiver cell or die. The electrical connection between the receiver die and the conductive pattern is often facilitated by a pair of punched thin metal foil or braided ribbon/mesh connectors which extend along and are welded or soldered to respective ones of opposed sides of the receiver die, which typically has a quadrangular or square configuration as indicated above. More particularly, the pair of punched thin metal foils or braided ribbon/mesh connectors are welded or soldered to respective ones of the bus bars on the top or front surface of the receiver die. In certain existing CPV modules, the electrical connection of the receiver die to the conductive pattern is facilitated by the use of multiple wires bonded to the bus bars on the front surface of the receiver die and the bond pads of the conductive pattern of the substrate, the wires being used as an alternative to the aforementioned braided ribbon or mesh interconnects. These wire bonds are often fabricated from gold, and are provided in differing numbers and/or diameters depending on the design of the CPV module. The CPV module may further include a light concentration means which is adapted to concentrate solar radiation onto the front surface of the receiver die.
Current CPV receiver die packages or modules typically generate up to ten amps of electrical current. In order to carry such high current, the above-described ribbons made of metal foil or braided wire mesh, or the above-described multiple bond wire bonds are used to form the interconnection between the bus bars on the front surface of the receiver die and the bond pads of the conductive pattern on the substrate. However, the use of the ribbon/mesh type interconnects or, alternatively, the bond wires give rise to certain deficiencies in currently known CPV modules which detract from their overall utility. More particularly, the ribbon/mesh type interconnects do not have good shape control for automatic pick up, and require the use of specialized welding equipment for the fabrication of the CPV module using the same. Stated another way, it is often difficult to control the shape of the ribbon/mesh type interconnects for automatic pick up and placement, with the fabrication process being mostly done through the use of special welding equipment or manual soldering which is more labor intensive and thus more costly. When bond wires are used as an alternative to the ribbon/mesh type interconnects, problems may arise in relation to current crowding if too few wires are used. Moreover, the use of bond wires (as well as the use of the soldered or welded ribbon/mesh interconnects) often gives rise to concerns regarding the electrical current carrying capability of the CPV module including the same.
The present invention addresses these and other shortcomings of prior art CPV modules by providing a CPV module wherein a conductive paste is used as an alternative to wire bonds or braided ribbon/mesh connectors to facilitate the electrical connectivity between the concentrated photovoltaic receiver cell or die of the CPV module and the conductive pattern of the underlying substrate thereof. In accordance with the present invention, the possibility of accidentally shorting the top of the receiver die with the other metal parts of the CPV module is avoided by molding at least the periphery of the receiver die with a mold body, and then dispensing or printing the conductive paste between the top of the receiver die and the substrate, the mold body defining a reservoir which facilities the flow of the conductive paste in a prescribed pattern. These and other features of the present invention will be described in more detail below.
Common reference numerals are used throughout the drawings and detailed description to indicate like elements.